Bacterial alkaline phosphatase (also known as PhoA) is derived from E. coli. It appears to require export to the periplasm to show enzymatic activity. Fusion of the secreted alkaline phosphatase to an integral cytoplasmic membrane protein of E. coli shows different activities depending on where with the membrane protein the alkaline phosphatase is fused. Consequently, analysis of alkaline phosphatase fusions to membrane proteins of unknown structure are generally useful in determining their membrane topologies.
